A multitude of wells have been drilled into earth strata for the extraction of oil, gas, and other material there from. In many cases, such wells are found to be initially unproductive, or may decrease in productivity over time, even though it is believed that the surrounding strata still contains extractable oil, gas, water or other material. Such wells are typically vertically extending holes including a casing usually of a mild steel pipe having an inner diameter of from just a few inches to over eight inches used for the transportation of the oil, gas, or other material upwardly to the earth's surface. In other instances, the wellbore may be uncased at the zone of interest, commonly referred to as an “openhole” completion.
In an attempt to obtain production from unproductive wells and increase production in under producing wells, methods and devices for forming a hole in a well casing, if present, and forming a lateral passage there from into the surrounding earth strata are known. For example, a hole in cased wells can be produced by punching a hole in the casing, abrasively cutting a hole in the casing, milling a hole in the casing wall or milling out a vertical section of casing. While more or less efficacious, such methods are generally familiar to those in the art. In openhole wells, the steps to form a hole in the casing are not required, but the methods for forming a lateral passage into the surrounding strata may be virtually identical to those used on cased well.
Under both the cased and uncased well scenarios, a type of whipstock is typically incorporated to direct the cutting head out of the wellbore and into the formation. The whipstock may be set on the end of production tubing. Because of the time and economic benefits, often the cutting tools are run on the end of coiled tubing. In at least one known conventional horizontal drilling method using coiled tubing, the cutting tool completes its transition to the horizontal direction over a radius of at least several feet and some methods require a radius of over 100 feet. The size of the radius stems primarily from the length and diameter of the cutting tools and the rigidity of the toolstring that must transition around the radius. Other known methods for creating horizontal drainage tunnels are able to transition a much tighter radius (e.g. within 4.5″ casing) by not attempting to pass relatively long and/or large diameter tools (e.g. a mud motor) outside of the wellbore. Instead most such methods utilize a flexible jetting hose with a specialized and relatively small nozzle head (e.g., less than a few inches long). Such methods may be efficacious, but typically suffer from a common problem that that they do not and/or cannot provide adequate torque to satisfactorily power a mechanical cutting means capable of cutting harder formation. Accordingly, these methods may be limited only to very soft formations.
Furthermore, most known methods and apparatus have also generally been unable to provide technically or commercially satisfactory results because of an accumulation of cuttings in the wellbore. Many known apparatus utilizing a form of jetting nozzles have been found unable to produce a satisfactorily large hole in the strata and, even when directed at soft strata, have been found to hang-up when trying to advance the nozzle into the formation.
Other known methods for creating a lateral borehole entail transferring torque from a motor through multiple discrete but connected drive segments around the whipstock to the cutting head. While such drive systems may be capable of cutting earthen formation they may suffer from one or more of the following shortcomings: they may be more costly than other solutions; they may allow for cuttings to become entrapped between the segments thereby disrupting the smooth operation of the system; and/or they suffer from being more time consuming and/or costly to service and repair.
In addition to the aforementioned, cuttings created from the lateral drilling process or materials in the wellbore can also be problematic. If the rat-hole of the wellbore (the portion beneath the work area) is not deep enough to accommodate these materials, the materials can fill the wellbore up to or above the elevation of the whipstock. This in turn, can effectively preclude the removal of cuttings from the lateral borehole being drilled as the cutting have nowhere to fall and hence cause a stop in forward cutting of the lateral borehole. Additionally, cuttings in the wellbore can fill-up so that repositioning of the whipstock—such as to a new zone of interest—movement of the whipstock cannot be done.
In view of the above, it would be desirable to have a cutting tool comprised of an essentially continuous flexible member capable of being run on a wireline unit, on coil tubing or on jointed tubing or rod, the tool capable of being run in a wellbore and of transitioning in an effective radius of less than about 36 inches to a substantially horizontal orientation, wherein the cutting tool is provided with sufficient torque to cut even hard formation, like dolomite. It would further be desirable to have a cutting system capable of rotating under the power of fluid and wherein the fluid may be emitted from the cutting tool to provide assistance in the removal of cuttings, to clean the cutting faces and/or to cool the cutting tool.